The text below simply represents a crude lecture outline of one of the topics covered in class. It
is not meant to substitute for attending lectures or ignoring the textbook. Additional material,
including line drawings, kodachromes, and more extensive information on life-cycles and basic
biology, will be supplied in the lectures.

TOPIC #7: Order: Echinostomatiformes

infect all classes of vertebrate

many species have no second intermediate host and metacercariae encyst
on vegetation

adults often fail to resemble one another. However, developmental
biology clearly reveals common ancestry

adults often, but not always, with spined or scaled tegument
(especially anteriorly)

Aberrant hosts (Parasites cannot successfully establish successful
infections). Includes sheep, goats, roe deer; bighorn sheep easily
killed. Hosts often die of acute tissue damage due to excessive migration
of flukes. Damage usually focused on liver, although perforation of
hepatic capsule and even other organs may occur

Dead-end hosts (Flukes successfully reach liver but only
rarely mature. If they mature, few eggs are produced and
they often do not reach the intestine). Includes moose, cattle, bison,
yak, horse, pigs, peccary, llama, Sika deer. Excessive fibrosis and
thick-capsule walls, resulting in the eggs not exiting. Flukes often fail
to pair and undergo extensive migration throughout liver.

Prevalence of flukes increases with host age; young are rarely
infected.

Most hosts have few worms. Mean intensity of infection is usually
less than 10 worms

Infections of 20-125 flukes sometimes seen

A few elk have been found with over 500 adult flukes

Older animals tend to have a few more worms in each capsule,
suggesting new flukes may be able to invade previously established
capsules

Spotty distribution of the parasite in cervids is thought to be due to
the widespread decline of white-tailed deer since the 16th century,
followed by reduced numbers of other cervids. This may have reduced the
geographic distribution to refuge populations

Original host thought to be white-tailed deer, where only 60-70% of a
population usually becomes infected with only 5-10 flukes per host. The
fibrous capsules are thin-walled, and eggs are easily released. Intensity
and prevalences tend to be higher in elk, more eggs are produced,
and more pathology is seen

Translocation of the parasite to other geographic localites in other
countries tends to be through elk where infections are more intense and
more eggs are produced

Domestic animals probably cannot maintain populations of the fluke in
the absence of cervids since few or no eggs are liberated into the
environment

Fasciola gigantica (found in a variety of Artiodactylids in
Africa, India, portions of Europe, Indonesia, Asia, and Hawaii. The most
common infections occur in cattle, sheep, and goats. Patent infections in
humans also occur). Hybrids between this species and Fasciola
hepatica have been reported.

Fasciola jacksoni (nasty pathology in Asian elephants)

Fasciolopsis buski (swine and humans in Asia)

Echinostoma spp. (family: Echinostomatidae)

Tend to be relatively non-host specific in semi-aquatic vertebrates (multiple
species in humans too)